Feline immunodeficiency virus (FIV) is a lymphocytopathic lentivirus associated with fatal immunodeficiency in cats. We have molecularly cloned a biologically active provirus and are in the process of determining the complete DNA sequence of this clone. A major objective of the proposed research is to elucidate molecular mechanisms regulating FIV gene expression in tissue culture systems. The hypothesis is that cell activation and proliferation signals are important factors regulating FIV gene expression and replication. FIV mRNA species will be identified in productively infected feline cell lines. Characterization of FIV transcripts in cell lines will provide a basis for analyzing the time-course of viral RNA synthesis and for elucidating the role of cellular physiology on viral gene expression. Temporal regulation of FIV transcription will be studied by analyzing synthesis of viral DNA, RNA, and polypeptides at various times after acute infection of feline cell lines. Transient expression assays will be used to determined whether or not FIV encodes genes that regulate (i.e., transactivate) viral gene expression. Cis-acting elements (targets) in the FIV genome that control viral gene expression will be localized. The role of cell proliferation on FIV replication and gene expression will be investigated in proliferating and resting feline cell lines. Cellular factors regulating FIV transcription will be identified. Patterns of FIV transcripts and polypeptides will be studied at various times after infection of activated feline T-lymphocytes and monocytes/macrophages. The extent of FIV replication and gene expression in cultures of resting (quiescent) T-lymphocytes will be analyzed and compared to that in activated cells. Information from these investigations on molecular aspects of FIV gene expression may be significant for understanding viral latency (or low-level persistent infection). In addition, these studies will lay a basis for elucidating viral determinants of pathogenesis; selected mutant viruses with modifications in cis- acting elements and trans-acting genes can be inoculated into cats to evaluate level of viremia, tissue distribution, and pathogenic potential. Results obtained from the proposed studies on FIV regulation will be compared with those on other lentiviruses including HIV and SIV. The FIV system may offer opportunities as an animal model to relate basic mechanisms regulating lentiviral gene expression with pathogenesis.